CVEs / CVE-2025-20333
CVE-2025-20333: Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow Vulnerability
- Known exploited in the CISA KEV catalog since 25 Sep 2025
- critical 9.9 CVSS 3.1 (from the CNA)
- EPSS 71.2% chance of exploitation in the next 30 days, higher than 99% of CVEs (30 Oct 2026)
- Last changed at its sources
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Summary
Cisco Secure Firewall Adaptive Security (ASA) Appliance and Secure Firewall Threat Defense (FTD) Software VPN Web Server contain a buffer overflow vulnerability that allows for remote code execution. This vulnerability could be chained with CVE-2025-20362.
Description
A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker to execute arbitrary code on an affected device. This vulnerability is due to improper validation of user-supplied input in HTTP(S) requests. An attacker with valid VPN user credentials could exploit this vulnerability by sending crafted HTTP requests to an affected device. A successful exploit could allow the attacker to execute arbitrary code as root, possibly resulting in the complete compromise of the affected device.
Affected and fixed versions
| Product | Affected | Fixed in |
|---|---|---|
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.1 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.1.5 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.1.7 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2.8 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2.14 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2.15 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2.17 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2.20 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2.24 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2.26 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2.28 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2.33 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2.35 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.2.38 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.3.8 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.3.11 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.3.14 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.3.16 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.3.18 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.3.21 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.3 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.3.26 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.3.29 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.4 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.4.3 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.4.7 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.4.8 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.4.10 | — |
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | 9.8.4.12 | — |
Exploitation
| In CISA KEV since | 25 Sep 2025 |
|---|---|
| Due date for US federal agencies | 26 Sep 2025 |
| Used in ransomware campaigns | Unknown |
| Required action | The KEV due date refers to the deadline by which FCEB agencies are expected to review and begin implementing the guidance outlined in Emergency Directive (ED) 25-03 (URL listed below in Notes). Agencies must follow the mitigation steps provided by CISA (URL listed below in Notes) and vendor’s instructions (URL listed below in Notes). Adhere to the applicable BOD 22-01 guidance for cloud services or discontinue use of the product if mitigations are not available. |
Severity
| CVSS 3.1 | 9.9 criticalCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:HScored by the CNA ([email protected]) |
|---|---|
| Weakness | CWE-120 |
References
- CVE-2025-20333 on NVD
- CVE-2025-20333 in the CISA KEV catalog
- https://www.cisa.gov/news-events/directives/ed-25-03-identify-and-mitigate-potential-compromise-cisco-devices (cited by CISA)
- https://www.cisa.gov/news-events/directives/supplemental-direction-ed-25-03-core-dump-and-hunt-instructions (cited by CISA)
- https://www.cisa.gov/eviction-strategies-tool/create-from-template (cited by CISA)
- https://sec.cloudapps.cisco.com/security/center/resources/asa_ftd_continued_attacks (cited by CISA)
- https://sec.cloudapps.cisco.com/security/center/private/resources/asa_ftd_continued_attacks#Details (cited by CISA)
- https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-webvpn-z5xP8EUB (cited by CISA)
- https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-webvpn-z5xP8EUB Vendor Advisory
- https://sec.cloudapps.cisco.com/security/center/resources/asa_ftd_continued_attacks Vendor Advisory
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-20333 US Government Resource
Sources
Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.
This product uses data from the NVD API but is not endorsed or certified by the NVD.